T1D glossary

Bolus

Also called bolus insulin, mealtime insulin, correction bolus.

A bolus is a single dose of rapid-acting insulin on top of basal insulin. A meal bolus covers carbohydrate and a correction bolus brings a high back toward target; many boluses are both. ADA describes insulin plans as basal, mealtime and correction insulin. (OpenAPS documentation; ADA Standards of Care 2026, section 9)

Formula

Bolus = meal part (carbs ÷ ICR) + correction part ((glucose − target) ÷ ISF), adjusted for IOB on most calculators

(ADA Standards of Care 2026, section 9)

Worked example

Arithmetic only: 45 g at ICR 15 g/U is 3 units; glucose 180 with target 120 and ISF 60 is 1 unit; no IOB. The calculator shows 4 units.

Related terms

• Basal insulin
• Insulin-to-carbohydrate ratio
• Insulin sensitivity factor
• Insulin on board
• Pre-bolus

Sources, quoted

• OpenAPS documentation: “Bolus - extra insulin given by a pump, usually to correct for a high Blood Glucose (BG) or for carbohydrates”
• ADA Standards of Care 2026, section 9: “Insulin replacement plans typically consist of basal insulin, mealtime insulin, and correction insulin”
• ADA Standards of Care 2026, section 9: “Mealtime and correction: URAA or RAA by bolus based on ICR and/or ISF and target glucose”

Every quote above is checked against its source page before each update of this site; last checked 2026-10-06. The worked example is our own arithmetic. This page explains a term; it is not advice for a person's treatment.